In the games

In the core series

In the Pokémon games, a Pokémon's level is determined by how much experience it has. A Pokémon's level will range from 1 to 100. When a Pokémon gains a level, its stats increase by a small amount. Depending on the exact level, it may also learn a new move or evolve. Opponent's levels may be viewed in-battle, and players may see their own Pokémon's levels in-battle, in the PC or by using the menu.

Using a Rare Candy will increase a Pokémon's level by 1 (and increase its experience accordingly).

In Generation IV, during battle, if a Pokémon almost has enough experience to level up, its Poké Ball will shake in the player's team summary.

In Generation I, if a Pokémon gains enough experience to gain more than one level, it will grow straight to the new level, and is unable to learn any move learned at a skipped level. In Generation II, the active Pokémon grows level by level, whereas switched out Pokémon grow straight to the new level (but are able to learn any moves regardless). From Generation III onwards, all Pokémon grow level by level.

In GenerationsIII and IV only, when a Pokémon has reached level 100, even if it has not gained maximum EVs, it cannot continue gaining EVs through battle (except Deoxys). Vitamins can still be used to raise EVs. In Generations I and II as well as from Generation V onwards, EVs can be gained even by level 100 Pokémon (although the Box trick is required in Generations I and II for the stats to update).

By exploiting the old man glitch in Generation I, a Pokémon can be acquired at a level higher than 100. Also in Generation I, any Pokémon can also be raised to a level above 100 via the Pokémon merge glitch; however, Pokémon in the Slow experience group need to be merged with a glitch Pokémon who requires even more experience at level 100. These Pokémon can continue to be leveled up with Rare Candies until level 255. Whenever a Pokémon over level 100 gains any experience, its level will revert to 100. If a Rare Candy is used on a level 255 Pokémon, it will revert to level 0 due to an overflow.

In Generations I and II, Pokémon were not legitimately available at a level below 2. This could be related to the fact that in Generations I and II, Pokémon in the Medium Slow experience group had a negative experience value at level 1, causing them to level up instantly to level 100 if they were to gain less than 54 experience points in battle (a high possibility on the games' early routes). Instead, Pokémon on the games' earliest routes were found level 2 or level 3, and starter Pokémon are given out at level 5. Likewise, Pokémon hatch from Pokémon Eggs at level 5.

From Generation III onwards, experience required to level up is taken from a lookup table, rather than by using a programmed equation as in Generations I and II; in Generation III, however, Pokémon still hatch from Eggs at level 5, and no wild Pokémon can be found at a level below 2. From Generation IV onwards, Pokémon hatch from Eggs at level 1 and some Pokémon are available in the wild at level 1 (however, starter Pokémon are still received at level 5).

Underleveled Pokémon

Through some unique circumstances, it is possible to have Pokémon at a lower level than they are usually available via evolution. Underleveled Pokémon appeared as early as Red and Green, with level 4-6 Kakuna and Metapod available in Viridian Forest. Kakuna and Metapod cannot be obtained by evolution until level 7.

An application of the Pomeg glitch in Emerald makes it possible to evolve a Pokémon while it is still inside an Egg, allowing any such evolved forms to be obtained at level 5. In Generation IV, this particular exploit of the Pomeg glitch was fixed; the Pomeg glitch was removed entirely in Generation V.

Disobedience

Outsider Pokémon (Pokémon obtained via trade or event distribution) occasionally disobey the player's commands if they are above a certain level. The Badges the player owns determine the maximum level outsider Pokémon can be before there is a possibility for them to disobey. Not owning the region's second Badge means that no traded Pokémon whose level is above 10 (level 20 in Generation VI) will obey the player; if the player has the region's eighth Badge, Pokémon will always obey.

In the spin-off games

In the Pokémon Mystery Dungeon series

In the Pokémon Mystery Dungeon series, level functions similarly to the core series. Like in the core series, each Pokémon's level, ranging from 1 to 100, depends on how much experience it has. When a Pokémon gains a level, its stats increase slightly and it may try to learn a new move. The moves that can be learned by each Pokémon, and the exact levels they will try to learn them, are the same as contemporaneous core series games. In order for some Pokémon to evolve, a minimum level is also required. However, evolution does not occur automatically, requiring access to specific places instead.

A number of dungeons across the series temporarily set the team's levels to 1 or 5 when entered. Their levels are restored to normal once the dungeon is exited.

In Pokémon Shuffle

Each Pokémon in Pokémon Shuffle has a level, which increases when it gains enough experience. As a Pokémon's level increases, its Attack power increases as well, with how much it increases per level determined by the Pokémon's Attack power at level 1. All Pokémon begin at level 1, with a maximum level of 10. However, Raise Max Level Enhancements are able to increase this cap for specific Pokémon, potentially up to level 20.

In the anime

The concept of levels of Pokémon is not as detailed, nor as frequently mentioned, in the anime. The first time levels were referred to was briefly by Meowth during the second episode when he said Ash's Pikachu was "powerful beyond its evolutionary level."

It was later mentioned more obviously by students at the Academy in The School of Hard Knocks. One of them was able to quote the levels at which Pidgey and the rest of its family evolve and learn certain moves, and another stated that Pikachu should be at least level 25. However, the main characters and their Pokémon remain seemingly oblivious to the idea.

In Roll On, Pokémon!, Ash's Pokédex mentions that the length a Donphan's tusks indicates its level, allowing Brock to deduce that the short-tusked Donphan they encountered was a young and low-level one.

Brock mentions in Doin' What Comes Natu-rally! that moves become more powerful as a Pokémon's level is raised; and Ash adds that the best way to raise levels is by battling. Despite this, Ash's most used Pokémon, Pikachu, doesn't show signs of being at a higher level than any other Pokémon. After appearing in more than 700 episodes, and battling in most of them, its level would be expected to be very high; however, at the start of each series of the anime, it either has as hard a time defeating other Trainers' Pokémon as his more recently-obtained Pokémon do or outright loses against them, an example being Trip's recently-obtained Snivy.

Dawn's Piplup also shows that the anime does not strictly follow the games' system. In its debut episode, it used Bide, a move Piplup normally does not learn until level 18, by which point it would be showing signs of evolution (which did not happen until Stopped in the Name of Love!). Therefore, level up moves can generally be learned at any time in the anime.

In the two MysteryDungeon specials, levels are mentioned, but not explained. This may mean that Pokémon themselves understand the concept of levels in the anime but humans do not.

In the manga

The concept of levels appears to be present within some manga (but not all of them).

In the Pokémon Adventures manga

At the end of every volume, or starting from Volume 15, at the end of certain rounds, the current levels of at least one of the main characters' Pokémon are given in a Pokédex or Adventure Map section.